The present invention relates to improvements in a throttle opening degree detection apparatus which detects a throttle opening degree on the basis of a signal outputted from a throttle sensor.
Generally, a throttle sensor, which outputs a signal according to an opening degree of a throttle value, outputs a dispersion including signal in a full close condition due to a dispersion of a sensor circuit or dispersion of an assembled position among individuals. Therefore, in case that the opening degree of the throttle valve is obtained on the basis of a difference between the full close reference value including dispersion and the output signal of the throttle sensor, it is necessary to cancel the dispersion of the full close reference value. Japanese Patent Publication No. 7-92138 discloses a method for canceling the dispersion of the full close reference value among individuals where an output signal of a throttle sensor under a condition that the throttle valve is mechanically put in a full closed condition is obtained by a leaning control as a learnt full close value. The leant full close value is used as a full close reference value to calculate the throttle opening degree so as to cancel the dispersion.
However, since the above-mentioned learning method is arranged to learn the output signal of the throttle sensor under a condition that the throttle value is mechanically put in a full close condition and to set it as the full close reference value, in case of a throttle value provided with a FIC (Fast Idle Cam) mechanism for directly opening and closing the throttle value in order to improve the starting characteristics in an engine cold condition, the throttle value may not be put in the full close condition due to the operation of the FIC mechanism. This operation of the FIC mechanism prevents the learning of the full close reference value and obliges to calculate the throttle opening degree on the basis of a previously stored initial value. Therefore, in case that the throttle opening degree is detected on the basis of the difference between the initial value of the full close reference value and the output signal of the throttle sensor, the opening degree of the throttle value under the opening operation of the FIC mechanism such as 0.5/8 opening degree is recognized as the throttle opening degree. Therefore, even when the driver does not depress an acceleration pedal, the conventional apparatus may recognize that the operation of the acceleration pedal is executed. This erroneous recognition may affect the control of the automatic transmission.